Multitouch input crashes Avalonia app on Raspberry Pi 4B / Linux (arm-x64)

[lubomirtrubac]

Describe the bug

Application with some dummy button (no event wired), hold with two fingers for a couple of seconds, sometimes needs more than one try. Application crashes to console with unhandled System.NullReferenceException. Tried on Raspbian x64 Lite using DRM and Raspbian x64 with full desktop - behavior is the same.

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
at Avalonia.Input.Gestures.PointerReleased(RoutedEventArgs ev)
at Avalonia.Reactive.LightweightObservableBase`1.PublishNext(T value)
at Avalonia.Interactivity.EventRoute.RaiseEvent(Interactive source, RoutedEventArgs e)
at Avalonia.Interactivity.Interactive.RaiseEvent(RoutedEventArgs e)
at Avalonia.Input.TouchDevice.ProcessRawEvent(RawInputEventArgs ev)
at Avalonia.RawEventGrouper.Dispatch(RawInputEventArgs ev)
at Avalonia.Controls.Platform.ManagedDispatcherImpl.RunLoop(CancellationToken token)
at Avalonia.Threading.DispatcherFrame.Run(IControlledDispatcherImpl impl)
at Avalonia.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
at Avalonia.Threading.Dispatcher.MainLoop(CancellationToken cancellationToken)
at LinuxFramebufferPlatformExtensions.StartLinuxDirect(AppBuilder builder, String[] args, IOutputBackend outputBackend, IInputBackend inputBackend)
at ARTRA.Dochadzka.Terminal.Desktop.Program.Main(String[] args)

To Reproduce

Steps to reproduce the behavior:

1. Follow steps to run Avalonia App on Raspberry Pi at: https://docs.avaloniaui.net/docs/guides/platforms/rpi/running-on-raspbian-lite-via-drm
2. Add a dummy button to the main view
3. Run application
4. Touch that button repeatedly with 2+ fingers
5. Application crashes

Expected behavior

Application should stay open

Environment

• OS: Linux - Raspbian x64 Lite / full with desktop
• Avalonia-Version: 11.0.7
• HW: Raspberry Pi 4B 8GB

[maxkatz6]

Should be fixed in the master: https://github.com/AvaloniaUI/Avalonia/pull/14140/files
Please try nightly builds.

[lubomirtrubac]

Thank you for your advice. No, it is not fixed in nightly builds, I have tried:
11.0.999-cibuild0043664-beta
11.1.999-cibuild0043666-beta
Both behave the same - using 2+ touches simultaneously and holding for a couple of seconds repeatedly crashes the app, now without any stacktrace info, just straight to console.

11.0.999
This version behaves a little differently - application just freezes and does not respond anymore.

[lsoft]

Looks like we see the same problem.

@lubomirtrubac does any workaround found?

[pkstrsk]

We are also experiencing the same problem, latest version of Avalonia.
Edit: Raspberry 5

[zabolotnev]

@maxkatz6 The problem is in Gestures.PointerReleased. In some cases value s_lastHeldPointer is null and s_isHolding is true. It looks like some kind of race condition, or unexpected order of calls. Anyway it causes NRE. I'll try to submit a PR today.

[lubomirtrubac]

@lsoft @pkstrsk Hello, unfortunately no - I did not even try to find a solution, because I had to implement other parts of the app first.
@zabolotnev Thank you for finding a solution. Hope it will be solved in upcomming release of Avalonia.

[maxkatz6]

Fixed by #15117